1. Field of the Invention
The present invention relates to an encapsulating system useful in inductive electrical devices, and more particularly, to a potting compound and a coil impregnant useful in a ballast for at least one gaseous discharge lamp.
2. Description of the Prior Art
Asphaltic materials, usually in the form of blown asphalts, have been accepted as potting compounds and coil impregnants and are presently in general use. While satisfactory in many applications, asphaltic materials have many limitations and are definitely deficient for many other applications.
A potting compound is often used in conjunction with a metal receptacle for encapsulating transformers, inductors and the like which generally are characteristically small size components. The physical property requirements of and considerations for such a potting compound are diverse; while some essential properties can be compromised, a successful compound must embody at least minimal and preferably the highest standard, in each of the following areas:
1. Sound suppression--Highly important is the sound suppression characteristic. The material should have a high degree of sound suppression of the sound level which might accompany normal operation of the electrical device. The purpose is to convert the sound of operation of the device into heat which in turn is dissipated by the potting compound, an important property when applied, for instance, to a ballast for fluorescent lighting;
2. Thermal conductivity--The potting compound should have a high rate of heat transferability since it must convey heat as rapidly and efficiently as possible away from the working components of the electrical device which has been encapsulated;
3. Water imperviousness--The potting compound should be relatively unaffected by water and should protect the components from the adverse effects of water; possess a low viscosity and should be pourable so as to completely fill the receptacle and totally encapsulate the electrical component. Almost immediately, upon contact with the cooler surface of the component and receptacle, the viscosity should increase so that the potting compound will not "run out" of openings and, during normal operation, should not exude from the receptacle;
5. Dielectric stability--Once formed as a potting compound, the material which protects the components should exhibit a high degree of inertness to the atmosphere, humidity and temperature changes so that the encapsulated electrical components are adequately protected. Though dielectric properties need not be high, they should be comparable to those of blown asphalts.
6. Cost--The potting compound must be reasonably priced both as a raw material and in its finished form;
7. Ease of repair--The potting compound should be capable of being removed by scraping and digging if repairs to the electrical components are required;
8. Energy consideration--Blown asphalts are derived from petroleum oils by methods well known in the art; in light of the rapid world consumption of petroleum and the dwindling supplies thereof and ecological concern, it is desirable that the potting compound be wholly comprised of, or at least based upon, a material which is not a petroleum derivative.
A coil impregnant, in addition to embodying the properties set forth in paragraphs 1, 2, 3, 4, 5, 6 and 8 above, should conform desirably to the following:
1. Should be able to wet the coils and flow between the laminations and coil turns so as not to leave any air bubbles;
2. Should be solderable with rosin flux; ie., without having to strip, mechanically or chemically, the impregnant material from terminals and wires to be soldered; and
3. Should, during manufacture of the device, not produce vapors which are photochemically active or otherwise deleterious to the environment.
Upon consideration of these requirements, it becomes apparent why the art only rarely yields an improved encapsulating system and why the asphaltic materials have enjoyed such a high degree of acceptability for such a long time. The problem of how to obtain an improved encapsulating system, ie, potting compound and coil impregnant having improved sound suppression capabilities has persisted and is an indication of the unobvious nature of the present invention.
It is desirable therefore to provide an encapsulating system including a potting compound and a coil impregnant wherein the above properties are maximized.
Accordingly, it is an object of the present invention to provide a new and improved potting compound which will supply certain of the deficiencies of the asphaltic compounds and in particular, a higher level of sound suppression.
Another object of the present invention is to provide an encapsulating system including a potting compound and a coil impregnant which will be sufficiently economical, both as a starting material and in method of application: ie, basically not a petroleum derived product.